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Make your holiday gatherings COVID-safer with rapid tests

Jon Healey, Los Angeles Times on

Published in Health & Fitness

How reliable are the results?

The coronavirus that causes the COVID-19 disease can take several days to build up steam (or "viral load"), which means you aren't likely to show symptoms or be infectious to others immediately after you've caught it. That's why public health officials advise you not to get tested immediately after you've been exposed to people who might be infectious.

Molecular tests, however, use chemical techniques to amplify the amount of genetic material in a sample, enabling them to detect the presence of the coronavirus at a very early stage — in some cases, even before a person can pass along the infection to others. On the other hand, they may also find leftover traces of the virus after a person is no longer contagious. And like any test, they are subject to contamination and other glitches that can cause erroneous results, including the occasional false positive. It's not common, but it's more likely to happen in communities that have few cases of the disease.

Antigen tests have proven to be as good as molecular tests at avoiding false positive results. And according to the CDC, these tests are also just as good when it comes to detecting COVID in someone who is showing symptoms of the disease, such as a cough, a fever and a sore throat.

Where the tests fall short, the CDC warns, is with people who have the virus but show no symptoms, especially if they're in the early stages of infection and may not yet have enough of a viral load to infect others. The agency recommends that people perform a second antigen test a few days after the first one, which is why the kits are sold as two-packs.

If you haven't been vaccinated and you've come into close contact sometime in the previous two weeks with someone who had COVID, the CDC recommends that you get a molecular test just to be sure you're not infected.

 

What's the best use of rapid tests?

Testing can reduce the risk in a variety of holiday scenarios, but Jha and Dr. Robert Wachter, chair of the department of medicine at UC San Francisco School of Medicine, said it makes the most sense in two situations: if unvaccinated people will be joining you for the holidays, or if people in your group would be at high risk of deadly complications if they contracted a breakthrough case of COVID-19. "Other than that, while it could render a gathering a smidgen safer, it doesn't feel worth it to me to spend a few hundred bucks testing 10 or so people," Wachter said in an email.

Another factor weighing in favor of testing is when there is a high rate of COVID infections in the community, Jha said. But which community determines the amount of risk? That may be hard to figure out if you have guests coming from several parts of the country.

When and how often you should take a test depends on the nature of the gathering. "Rapid tests are a measure of contagiousness," Jha said, "and so you want to test as close as you can of getting together with people." If it's just a Thanksgiving day meal, Jha said, "The ideal situation would be to test on Thursday morning."

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